Contents lists available at ScienceDirect Journal of African Earth Sciences journal homepage: www.elsevier.com/locate/jafrearsci Characterizing coal seams hosted in Mmamabula Coalfield, central Botswana using pseudo-3D electrical resistivity imaging technique Bokani Nthaba a,b , Elisha Shemang a,∗ , Amogelang Hengari a , Boniface Kgosidintsi a , Takeshi Tsuji b a Earth and Environmental Sciences Department, Botswana International University of Science and Technology, P/Bag 16, Palapye, Botswana b Earth Resources Engineering, Kyushu University, Fukuoka, Japan ARTICLE INFO Keywords: Coal seams Electrical resistivity imaging Isosurface Mmamabula Coal field Middle Ecca subgroup ABSTRACT We used 2D and 3D electrical resistivity imaging (ERI) data inversion to locate and characterize the coal seams in Mmamabula Coalfield. The 2D ERI data inversion usually assumes that subsurface geological units (e.g. coal seams) are infinitely continuous in the direction perpendicular to the profiles. However, this assumption might be violated due to the heterogeneous nature of fluvial/deltaic environments. The lateral variation of the sub- surface material can be effectively determined in 3D ERI inversion models. In this study, 2D ERI data were acquired along ten parallel profiles trending north-south, then inverted to produce 2D and 3D models. From the 2D ERI inversion results, we observed that the shallower coal seam occurs around a consistent depth of 13.6 m whereas the second observable coal seam occurs at variable depths including at 50 m and 60 m along the two profiles. Discontinuities in coal seams were also identified. However, the information provided by 2D data inversion in such an environment is insufficient to determine the geometry of coal seams as well as to produce accurate and precise resource estimates for future exploitation. As an alternative, 3D data inversion gives better insight on the subsurface geology complexity and significantly resolves the geometry of coal within the study area. The presented 3D inversion results indicate that coal seams are intermittent and alternate well with other coexisting sedimentary units. We also deduced that they trend east-west and are split and adjoined in some areas along the north-south direction. Overall, 3D data inversion result resolves the elongated coal seams in Mmamabula Coalfield and reveals additional information that cannot be determined on 2D ERI inversion results. 1. Introduction Coal is an organic sedimentary rock that forms from the accumu- lation and preservation of plant materials buried millions of years ago, usually in swampy environments. Coal is the world's most abundant fossil fuel with approximately 990 billion tonnes of coal reserves (BGR, 2009). Coal fuels ~42% of global electricity production, and is still expected to fill a significant role in meeting electricity demands well into the foreseeable future, especially with the growing demand in developing countries (Mohammed et al., 2016). In Botswana, the coal resources require detailed exploration and evaluation, with current coal reserves estimated to be 212 billion tonnes (Grynberg, 2012). Once proven, these figures are likely to make Botswana one of the world's largest producers of coal. Despite multiple discoveries of coal reserves in Botswana, only one coal mine (Morupule) is operating at present. Due to the current instability in mining and insufficient energy supply to the nation it is necessary to study the unexploited Mmamabula coal reserve, which is reported to host coal deposits of identical grade (sub- bituminous to bituminous) to those at Morupule (Grynberg, 2012). As such, to assess and manage coal resources in green-fields (e.g. Mma- mabula coal field) and in operational sites (e.g. Morupule), it is ne- cessary to develop a good insight of the nature and distribution of the coal resources in those sites. The use of exploration geophysics is not only limited to detecting new coal deposits, its application extends to assessing the nature of new or existing deposits to determine the quantity and quality of the coal contained. The techniques used in exploration geophysics also play a key role in detecting intrusive dykes and sills, as well as in identifying structural and in-seam discontinuities such as faults and lenses (Van Schoor and Fourie, 2014) which may adversely impact the future mining operations. The successful application of surface geophysical measurements for these purposes relies on the existence of suitable contrasts between the physical properties of target strata and those of surrounding materials (Green et al., 1988; Johnson–D’Appolonia, 2003). The unique physical properties of coal make it a suitable target for detection by geophysical methods. Coal is distinct from other https://doi.org/10.1016/j.jafrearsci.2020.103866 Received 7 February 2020; Received in revised form 24 April 2020; Accepted 25 April 2020 ∗ Corresponding author. E-mail address: shemange@biust.ac.bw (E. Shemang). Journal of African Earth Sciences 167 (2020) 103866 Available online 04 May 2020 1464-343X/ © 2020 Elsevier Ltd. All rights reserved. T